Question

I wrote an android app that solves quadratic equations and then is supposed to graph them. The library I am using requires the data sets to be in ArrayList form. However the loop I have to create the array involves adding a double to them which you cannot do with array lists. Here is the code:

List<double[]> x = new ArrayList<double[]>();
List<double[]> values = new ArrayList<double[]>();
QuadraticActivity c = new QuadraticActivity();


x=(c.xValueArr);
values=(c.yValueArr);

for (; c.xCurrent <= c.xEnd; c.xCurrent += c.xStep) {
    double yCurrent = (c.a)*Math.pow(c.xCurrent, 2) + (c.b)*c.xCurrent + (c.c);
    c. xValueArr .add ((c.xCurrent));
    c. yValueArr .add ((yCurrent));

Answer 1

Judging from your code, c.xValueArr and c.yValueArr are of type, double[]. If so, then just change the first 7 lines of code to this:

QuadraticActivity c = new QuadraticActivity ();
ArrayList<Double> x = Arrays.asList (c.xValueArr);
ArrayList<Double> values = Arrays.asList (c.yValueArr);

Note: You’re instantiating two new ArrayLists in lines 1 and 2 but are replacing them in lines 6 and 7. Also, you’ll have to add the new values inside the loop manually, as x and values don’t point to the same arrays as c‘s arrays. A better fix would be to declare and initialize x and values after the iteration, but since you didn’t include a closing }, I’m assuming you need them in the iteration.